Metal nanoparticle enhanced semiconductor film for functionalized textiles

ABSTRACT

A method for forming a metallic nanoparticle and semiconductor coated fiber material is provided. The method can include the steps of coating at least one surface of a material, for example a textile material, with a semiconducting layer, and growing metallic nanoparticles on the semiconducting layer. The steps for coating the surface of the material with a semiconducting layer can include forming a titanium dioxide film on the surface of the textile material. The steps for forming metallic nanoparticles on a semiconducting layer can include immersing the coated textile layer in a metallic nanoparticle precursor solution, drying the coated textile layer and exposing the textile layer to UV radiation. The metallic nanoparticles can include gold and/or silver nanoparticles. Also disclosed are materials having a least one treated surface coated with metallic nanoparticles. The treated surface may comprise the surface of a textile material treated according to the methods provided herein.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support underD01_W911SR-14-2-0001-0003 awarded by the Department of Defense. Thegovernment has certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

None

FIELD OF THE INVENTION

This invention relates to the field of surface coatings and methods forproviding a surface coating to a material, as a method of treating amaterial, for example a textile material, such that at least one surfaceof the material comprises a nanostructured coating is provided. Theinvention also relates to the field of nanostructured coatings that areself-cleaning, anti-microbial, and radiation-protective. The inventionfurther relates to the field of semiconducting metal oxide thin filmcoatings, as semiconducting metal oxide thin film coating comprisingmetallic nanoparticle incorporated to a semiconducting film is provided,the film providing an active photocatalyst layer imparting the abovecharacteristics to a surface having the film provided thereon. Theinvention also relates to the field of methods for providing a thin filmto a surface, as a method for generating a thin, homogenous,nanostructured film of titanium dioxide on a cellulosic substrate andgenerating noble metal nanoparticles (silver and gold) directly on thetitanium oxide surface to provide a treated surface is provided. Thetreated surface enhances photocatalytic activity at the surface, andrenders the treated surface self-cleaning and antimicrobial. A surfacetreated with a titanium dioxide coating process alone does not possessthese characteristics. The invention also relates to methods of treatingmaterials and surfaces of other natural or synthetic substrates, othersemiconductor-based thin films, and other noble/common metallicnanoparticles.

BACKGROUND OF THE INVENTION

Conventional fabric treatment methods aim to provide stain resistance,extend the lifetime of the textile material, or provide anti-microbialaction through the use of chemicals that seal and protect the fabric, orthrough treatment methods that leave the fabric innately resistant tostains. Treatment methods that rely on semiconducting materials beingdeposited on a textile typically rely on complicated methods ill-suitedto scaling to industrial scale, and also typically yield a textilematerial that is impregnated by and/or decorated with discretesemiconductor nanotubes or nanoparticles, which both have thedisadvantage of being more readily removed from the fabric and lessphotocatalytically active than a thin, uniform film. Sol-gel basedtreatment techniques are one of the developed procedures for depositinga surface photocatalytic coating on textile materials.

While advancements have been made in the development of advanced textilematerials with a photocatalytic film or layer, current methods andtechniques are inadequate because they are ill-suited to large scaleproduction and they have limited self-cleaning, anti-microbial, andradiation-protective properties. Accordingly, a need exists for animproved advance textile or fiber materials with self-cleaning,anti-microbial, and radiation-protective properties that overcome theaforementioned problems.

SUMMARY OF THE INVENTION

The method and system of this invention center around the innovativeconcept of methods for generating a nanostructured photocatalytic systemon at least one surface of a material, for example a textile material,using simple, scalable methods. The invention allows a nanostructuredphotocatalytic system to be constructed using a sol-gel based syntheticmethod for depositing a semiconducting thin film that coats the fabric,provides a surface for photocatalytic chemical reactions to occur, anditself absorbs UV light preventing the penetration of the material by UVradiation. Noble metal nanoparticles are grown on this semiconductingsurface by a solution-based coating method followed by irradiation withUV light which, together with the already deposited semiconductinglayer, acts to reduce the noble metal precursors, and generatenanoparticles on the semiconducting surface. These nanoparticles arevariably sized, which allows for the absorption (and thus thephotochemical utilization) of a range of incident radiation thatwouldn't be absorbed by the semiconducting oxide layer alone. Thesenanoparticles are also capable as acting as electron acceptors for thephoto-generated electrons from the oxide surface, which absorbs incidenthigh-energy UV radiation. The nanoparticles thus help to reduce chargerecombination and also generate additional excitons from the absorptionof incident light at a longer wavelength than that absorbed by thesemiconducting material. The tandem semiconducting oxidelayer/nanoparticle system exhibits more efficient photocatalyticperformance than other methods, and the synthetic techniques used inthis invention are facile and scalable.

According to one embodiment of the present invention, a method isprovided for the deposition of thin, uniform semiconducting films andsubsequent decoration of said film with noble metal nanoparticles growndirectly on the semiconducting film surface.

According to one embodiment of the present invention, this methodprovides a means for the large-scale facile manufacture of textilematerials with said coating, which lends the finished materialsself-cleaning, antimicrobial, and UV-protective properties.

According to one embodiment of the present invention, a method isprovided for the direct reduction of gold chloride and silver nitrate(gold and silver nanoparticle precursors) on the semiconducting surfaceunder intense UV radiation during the manufacturing process, thusenabling the direct growth of the nanoparticles on the oxide surface andimproving manufacturing time compared to the utilization of variouschemical reducing agents and/or the separate growth of the nanoparticlesand subsequent deposition onto the semiconductor-coated fabric, whichwould further complicate manufacture.

According to one embodiment of the present invention, a method isprovided for coating all fibrous/non-fibrous textile materials with asemiconducting layer and nanoparticles to lend them anti-microbial,self-cleaning, and radiation-protective properties.

The present invention advances the art of treating textile materialswith the aim of obtaining a textile material that has self-cleaning,anti-microbial, or radiation protective properties, and, in addition,provides an improved method for the application of the coating in ascalable manufacturing process.

Other aspects and advantages of the present invention will be apparentfrom the following detailed description of the preferred embodiments ofthe accompanying drawing figures.

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

A clear understanding of the methodology employed and results obtainedby this novel treatment technique can be had by referencing the appendeddrawings which illustrate the method and results of the innovativetreatment technique, although it will be understood that such drawingsdepict preferred embodiments of the invention and, therefore, are not tobe considered as limiting its scope with regard to other embodimentswhich the invention is capable of contemplating.

Accordingly, in the accompanying drawing, which forms a part of thespecification and is to be read in conjunction therewith in which likereference numerals are used to indicate like or similar parts in thevarious views:

FIG. 1 is a schematic representation of a methodology used to constructa metallic nanoparticle semiconducting film-coated textile material inaccordance with one embodiment of the present invention;

FIG. 2 is a schematic representation of a methodology used to depositthe semiconducting film onto a textile material in accordance with oneembodiment of the present invention;

FIG. 3 is an SEM image showing an uncoated pristine fiber material atlow and high magnification (a, b) and a TiO₂ coated fiber material atlow and high magnification (c, d) in accordance with one embodiment ofthe present invention;

FIG. 4A is a schematic representation of a methodology used to depositand/or grow metallic nanoparticles directly on the surface of fibermaterial having a semiconducting layer coated thereon in accordance withone embodiment of the present invention;

FIG. 4B is a schematic representation of a methodology used to depositand/or grow metallic nanoparticles directly on the surface of fibermaterial having a semiconducting layer coated thereon in accordance withanother embodiment of the present invention;

FIG. 5 is a SEM image showing an Ag—TiO₂ coated fiber material at lowand high magnification (e, f) and an Au—TiO₂ coated fiber material a lowand high magnification (g, h) in accordance with one embodiment of thepresent invention;

FIG. 6 is a graph containing the ultraviolet and visible absorptionspectra of an uncoated pristine fiber material, a TiO₂ coated fibermaterial, an Ag—TiO₂ coated fiber material, and an Au—TiO₂ coated fibermaterial in accordance with one embodiment of the present invention;

FIG. 7 is a graph showing XRD spectra for (a) pre-exposure Ag—TiO₂coated fiber material, (b) pre-exposure Au—TiO₂ coated fiber material,(c) pre-exposure TiO₂ coated fiber material, (d) pre-exposure pristineuncoated fiber material, and (e) post-exposure TiO₂ coated fibermaterial in accordance with one embodiment of the present invention;

FIG. 8 is a graph showing the ultraviolet and visible absorption spectraof (a) Ag—TiO₂ coated fiber material, (b) Au—TiO₂ coated fiber material,(c) TiO₂ coated fiber material, and (d) pristine uncoated fibermaterial, after staining with methylene blue dye and exposure tosimulated solar light (1.5 sun intensity) over a measured interval oftime to quantify the self-cleaning efficacy in accordance with oneembodiment of the present invention;

FIG. 9 is a graph showing the rate of stain extinction of (a) Ag—TiO₂coated fiber material, (b) Au—TiO₂ coated fiber material, (c) TiO₂coated fiber material, and (d) pristine uncoated fiber material, afterstaining with methylene blue dye and exposure to simulated solar light(1.5 sun intensity) over a measured interval of time in accordance withone embodiment of the present invention;

FIG. 10 is a graph showing the C/CO data for a Ag—TiO₂ coated fibermaterial over repeated cycles of staining and UV exposure in accordancewith one embodiment of the present invention;

FIG. 11 is a graph of the FTIR spectra for Au—TiO₂ coated fiber materialafter repeated exposure to simulated solar light for exposure times of(a) no exposure, (b) two hours, (c) four hours, (d) six hours, and (e)ten hours in accordance with one embodiment of the present invention;

FIG. 12 is an image of a Kirby-Baur disk diffusion test forantimicrobial activity with (a) Au—TiO₂ coated fiber material, (b)Ag—TiO₂ coated fiber material, and (c) pristine uncoated fiber materialin accordance with one embodiment of the present invention; and

FIG. 13 is a schematic representation of the antimicrobial activity ofAu—TiO₂ coated fiber material before and after light exposure inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with reference to the drawingfigures, in which like reference numerals refer to like partsthroughout. For purposes of clarity in illustrating the characteristicsof the present invention, proportional relationships of the elementshave not necessarily been maintained in the drawing figures.

The following detailed description of the invention references specificembodiments in which the invention can be practiced. The embodiments areintended to describe aspects of the invention in sufficient detail toenable those skilled in the art to practice the invention. Otherembodiments can be utilized and changes can be made without departingfrom the scope of the present invention. The present invention isdefined by the appended claims and the description is, therefore, not tobe taken in a limiting sense and shall not limit the scope ofequivalents to which such claims are entitled.

The present invention is directed to gold and/or silver titanium dioxidecoated fibers or textile materials 10. Such fibers 10 of the presentinvention have been shown to have substantial benefits, including beingself-cleaning, anti-microbial, and protective against UV radiation. Thepresent invention is also directed to a method 100 for constructingmetallic nanoparticle and semiconductor layer textile materials.According to one embodiment, method 100 includes procedures fordepositing and/or growing gold/silver nanoparticles onto ananostructured titanium dioxide (TiO₂) film applied to a textilematerial or fiber surface. As described in greater detail herein, themethod 100 of the present invention can be utilized to apply a uniformand high surface area film of TiO₂ onto a cotton fiber or other textilematerial, and subsequently directly incorporate gold/silvernanoparticles on the nanostructured TiO₂ surface of the fiber/textilematerial. The method 100 described herein can produce a TiO₂ film thatis substantially homogenous with uniformly distributed Au/Agnanoparticles on the TiO₂ film distributed using photocatalyticreduction method.

According to one embodiment the Ag—TiO₂ coated textile material 10 ofthe present invention was observed to have the largest improvement inrate of stain extinction compared to the untreated fibers with amethylene blue stain. According to one embodiment, the Au and/or Ag—TiO₂coated textile material 10 of the present invention were observed tohave the largest improvement versus untreated fibers when stained withCongo red. The Ag/Au—TiO₂ coated textile material 10 can maintainconsistent photocatalytic activity over multiple cycles and haveresistance to degradation, which was verified using Fourier transforminfrared spectroscopy (FTIR). The Ag/Au—TiO₂ coated textile material 10are also configured for efficient anti-microbial activity, which wasconfirmed by exposure of the fibers to bacterial culture (EscherichiaColi) and direct observation of antimicrobial activity.

As described herein, the present invention is directed to a method 100for depositing and/or growing nanostructured gold and silvernanoparticles on the surface of natural fibers (i.e., textile materials)that have been coated with TiO₂. The TiO₂ coating can be appliedutilizing a sol-gel based method that uniformly coats the fibermaterial; however, other methods can also be suitably be used. TiO₂ is awell-known photo-catalyst that has been extensively tested and shown toeffectively decompose a wide range of organic substances underirradiation with solar light, including methylene blue,isothiazolin-3-ones, formaldehyde, acid orange, phenol, coffee/winestains, and even the chemical warfare agent Soman. The innatephotocatalytic effectiveness of TiO₂ is very high, even under artificialroom lighting a layer of TiO₂ possesses sufficient photocatalyticactivity to completely mineralize an approximately 1 μm thickhydrocarbon layer every hour, and therefore can be suitable for asurface photocatalytic coating to produce self-cleaning fibers andtextile materials.

The gold and silver nanoparticles can be applied via direct reduction ofAuCl₃ and/or AgNO₃ by UV radiation as described herein. Ag/Au—TiO₂coated fibers 10 created through method 100 of the present inventionhave demonstrated self-cleansing and anti-microbial properties. Silvernanoparticles have been shown to have antibacterial activity and havebeen shown to reduce the incidence of electron/hole recombination whenused in conjunction with TiO₂, which should improve photocatalyticactivity. Gold nanoparticles have been shown to decrease the bandgap ofTiO₂ which improves overall photocatalytic activity and allows for thephotocatalytic destruction of certain organic under visible-only/UVfiltered lighting conditions where a TiO₂ coating alone is ineffective.As described herein, method 100 of the present invention is directed toprocedures for successfully depositing and growing gold and silvernanoparticles onto a TiO₂ coating layer that coats the surface of atextile or fiber material.

Referring to FIG. 1, method 100 according to one embodiment of thepresent invention is illustrated schematically. As shown, method 100begins with an initial step 200 that includes providing a fiber/textilematerial and coating the textile material with a TiO₂ coating. Asfurther shown in FIG. 1, method 100 includes a subsequent step 300 thatincludes depositing gold and/or silver nanoparticles onto the surface ofthe TiO₂ fiber/textile material. Method 100 and steps 200 and 300incorporated into method 100 for providing an Au/Ag—TiO₂ coated fibermaterial 10 will now be described in greater detail with reference tothe several figures.

Referring to FIG. 2, step 200 and the methodology for coating the fiberor textile material (referred to herein as a fiber material forsimplicity) with a thin film of titanium dioxide via a sol-gel methodcan take place in several steps as described below. At step 202, thefiber material can be washed and cleaned. According to one embodimentthe fiber material at step 202 can be thoroughly cleaned via washingwith acetone at an elevated temperature for a suitable period of time(e.g., hours) to remove any impurities that may be present (such asnatural fats). In other embodiments, any suitable cleaning method canalso be utilized. Next, at step 204, the fiber can be dried. Accordingto one embodiment, the drying process of step 204 can include drying thefiber material at room temperature or other suitable temperature for asuitable period of time (for example, 12 hours).

Next, at step 206, a TiO₂ nanosol coating solution can be prepared forcoating the fiber material. The coating solution can include thepreparation of two solutions: solution A and solution B. As shown bystep 206A, solution A can be prepared by combining approximately 2% byvolume acetic acid and 12% by volume titanium isopropoxide inapproximately 86% by volume 2-propanol and mix vigorously forapproximately 30 minutes as represented by step 206C. According to oneembodiment, solution A can comprise 50 mL of 2-propanol, 1 mL of aceticacid, and 5.91 mL of titanium isopropoxide; however, it is recognizedthat other percentage-by-volume amounts can suitably be used. As shownby step 206B, solution B can be prepared by combining approximately 6%by volume of concentrated hydrochloric acid and approximately 1.5%ultrapure water in approximately 92.5% of 2-propanol and mix vigorouslyfor approximately 30 minutes as represented by step 206C. According toone embodiment, solution B can comprise 50 mL of 2-propanol, 3 mLconcentrated hydrochloric acid, and 0.72 mL of ultrapure water; however,it is recognized that other percentage-by-volume amounts can suitably beused.

Next, at step 208, solutions A and B can be mixed together and combined.According to one embodiment, step 208 includes the procedure of slowlyadding solution B into solution A while under vigorous stirring (e.g.,400-800 rpm) solution A until the solutions A and B are thoroughlycombined to form the nanosol coating solution.

Next, at step 210, the fiber material can be immersed in the nanosolcoating solution for approximately 30 seconds and removed. Depending onthe particular application of method 100, the prepared nanosol coatingsolution can continued to be used for as long as 7 days before it losesits integrity and precipitating out TiO₂ and becoming qualitativelyopaque instead of transparent. The ability to reuse the prepared nanosolcoating solution for an extended period of time and provide cost andefficiency benefits for large-scale productions of Au/Ag—TiO₂ coatedfiber material 10.

Next, at step 212, the fiber material can be dried. According to oneembodiment, the drying process at step 212 can include drying the fibermaterial for approximately 24 hours at room temperature under normalatmospheric conditions.

Next, at step 214, the fiber material can be calcined in order to removeany residual solvent. According to one embodiment, as shown in FIG. 2,step 214 can include a sub-step 214A where the fiber material iscalcined at approximately 65° C. for approximately 10 minutes and asub-step 214B where the fiber material is calcined at approximately90-95° C. for approximately 5 minutes under normal atmosphericconditions.

Next, at step 216, the calcined fiber material can be hydrothermallytreated to remove excess oxide left behind from the nanosol coatingprocess. According to one embodiment, the process at step 216 caninclude boiling the fiber material in ultrapure water for a period ofapproximately 3 hours.

FIG. 3 illustrates the effect of the TiO₂ coating process described instep 200. FIGS. 3(a) and 3(b) provide SEM images at low and highmagnification, respectively of a cotton fiber material that was nottreated with the TiO₂ coating of step 200. FIGS. 3(c) and 3(d) provideSEM images at low and high magnification, respectively, of a TiO₂ coatedcotton fiber material that was treated with the TiO₂ coating of step200. The differences between (a) and (b) of FIG. 3 and (c) and (d)demonstrate how the coating process of step 200 creates a thin,essentially uniform coating on the surface of the fiber material, andthat the coating process of step 200 results in quality adhesion of thecoating to the surface of the fiber material without significantcracking or other surface deformities. The coating process of step 200can also result in a coating that is thin enough so as to allow forflexing of the fiber material without the coating cracking or becomingseparated from the fiber material surface.

Referring to FIGS. 4A and 4B, step 300 of the method 100 forconstructing Ag/Au—TiO₂ coated fibers 10 is described in greater detail.As schematically illustrated in FIG. 4A and described below, step 300can include several steps for depositing/growing gold and/or silvernanoparticles on the surface of the TiO₂ coated fiber material. Step 300can begin at step 302 where a metallic nanoparticle precursor solutionis prepared. According to one embodiment, the precursor is prepared bydiluting a solution of gold chloride (AuCl₃) with ultrapure water tocreate a 100 mL precursor solution of 1 mM AuCl₃. According to anotherembodiment, the precursor is prepared by diluting a solution of silvernitrate (AgNO₃) in ultrapure water to create a 100 mL precursor solutionof 1 mM AgNO₃. In other embodiments, greater or lesser concentrations ofgold chloride or silver nitrate can suitably be used to for theprecursor solution.

Next, at step 304, the TiO₂ coated fiber material can be immersed in theprecursor solution for a suitable period of time and then removed.According to one embodiment, the preferred time period is approximately30 seconds.

Next, at step 306, the metallic nanoparticle-TiO₂ coated fiber material(i.e., AuCL₃-TiO₂ coated fiber material or AgNO₃—TiO₂ coated fibermaterial) can be allowed to dry for a suitable period of time. Accordingto one embodiment, during step 306, the coated fiber material is left todry at room temperature under normal atmospheric conditions forapproximately 24 hours (however, other temperatures, conditions and timeperiods can also be suitably used during step 306).

Next, at step 308, the metallic precursor solution-TiO₂ coated fibermaterial is exposed to UV radiation for a suitable period of time asshown in FIG. 4A. According to one embodiment, the AuCL₃ or AgNO₃—TiO₂coated fiber material is exposed to approximately 254 nm UV radiationfor approximately 30 minutes. According to one embodiment, the UVradiation is applied for approximately 15 minutes on each side of thecoated fiber material as shown in FIG. 4B. Other suitable time periodsfor UV radiation exposure can also be suitable used in alternativeembodiments. Step 308 can act to photocatalytically reduce the metallicnanoparticle precursors deposited via a solvent-based method, and canessentially activate the photocatalytic surface. The semiconductingoxide material (TiO₂) is most photocatalytically active and/or capableof reducing the metallic nanoparticle precursors when irradiated with UVlight, so intense UV light can be preferable used for initial creationof the nanoparticles.

FIG. 5 illustrates the effect of the metallic nanoparticle applicationprocess described in step 300 where metallic nanoparticles (e.g., Au orAg nanoparticles) are deposited and/or grown the TiO₂ coated surface ofthe fiber material. As shown in FIGS. 3(a) and (b) and described above,the fiber material includes natural surface folds, which increase theexposed surface area of the fiber material and can improvephotocatalytic efficiency by providing more sites for photoreactions totake place and for the anchoring of nanoparticles. As shown in FIGS.3(c) and (d), the application of the TiO₂ coating on the surface of thefiber material results in a slight reduction in the fold definition.Subsequently, as illustrated in FIGS. 5(e)-(h), after the TiO₂-coatedfiber material is immersed in the metallic nanoparticle precursorsolution, removed, dried and exposed to UV radiation through steps302-308, the growth of metallic nanoparticles gold and silvernanoparticles on the TiO₂ coated fiber materials is visible on the SEMimages of FIG. 5. FIGS. 5(e) and (f) show Ag—TiO₂ coated fiber material10 at low and high magnification, respectively, while FIGS. 5(g) and (h)show Au—TiO₂ coated fiber material 10 at low and high magnification,respectively.

Referring to FIG. 6, the UV-Visible absorption spectra of Ag/Au—TiO₂coated fiber materials 10 prepared following the steps of method 100outlined above is shown, and the clear offset of the gold and silvernanoparticle coated fiber material is visible. As shown in FIG. 6, therelatively wide absorption peaks of the gold and silver nanoparticlepeaks is due to the range of nanoparticle sizes generated by thereduction method used above. Peak width and peak offset can be bothimportant for the photocatalytic efficacy of the textile coating. It isapparent that the absorption contribution of the nanoparticles allowsthe semiconducting layer to absorb incident near-UV/visible photonswhich enhance the photocatalytic efficiency.

FIG. 6 illustrates the development of Au and Ag nanoparticles under UVradiation where the Ag/Au—TiO₂ coated fiber materials 10 were formedusing 5 mM precursor solutions of AgNO₃ and AuCl₃. The gold peak in theembodiment illustrated in FIG. 6 is at 547 nm, which matches what wouldbe expected if the gold nanoparticles took on roughly spherical shapesand have an average size of 60-80 nm (calculated utilizing availabledata concerning nanoparticle size and max wavelength of UV-visabsorption). Further, the width of the peak indicates that nanoparticlesconstituting a range of sizes were directly generated on the TiO₂surface coating. The silver nanoparticle peak in the embodimentillustrated in FIG. 6 is at 440 nm, which matches what would be expectedif the average size of the nanoparticles were between 40 and 50 nm. Theintense absorption present in the UV-vis spectra of all TiO₂ coatedsamples in the UV region is due to the absorption profile of plain TiO₂.Because the gold and silver nanoparticle peaks occur in the visibleregion of the spectra it should be noted that the fiber materials maytake on a characteristic purple (in the case of gold) or brown (in thecase of silver) color after deposition of the nanoparticles but prior tostaining, which matches the coloration found in the literature whendealing with comparatively large gold and silver nanoparticles. FIG. 6further illustrates UV protective properties of the Ag/Au—TiO₂ coatedfiber materials 10 over untreated cotton, as the absorption of allsamples but pristine can be seen to dramatically increase in the UVregion of the spectra.

FIG. 7 illustrates the XRD spectra for (a) pre-exposure Ag—TiO₂ coatedfiber materials, (b) pre-exposure Au—TiO₂ coated fiber materials, (c)pre-exposure TiO₂ coated fiber materials, (d) pre-exposure pristineuncoated fiber materials, and (e) post-exposure TiO₂ coated fibermaterials.

FIG. 8 illustrates the UV-Vis absorption spectra of (a) Ag—TiO₂ coatedfiber materials, (b) Au—TiO₂ coated fiber materials, (c) TiO₂ coatedfiber materials, and (d) pristine uncoated fiber materials afterstaining with methylene blue dye and exposing the fiber material tosimulated full-spectrum solar light (1.5 sun intensity) over a varietyof time intervals. The area contained by the peak can be directlyrelated to the intensity of the appearance of the stain on the fibermaterial and thereby also to the concentration of the dye moleculesremaining on the surface of the Ag/Au—TiO₂ coated fiber materials byBeer's law. As also shown in FIG. 8, the rate of stain extinction/fiberself-cleaning is dramatically increased on the Ag/Au—TiO₂ coated fibermaterials as the methylene blue stain is being destroyed by theAg/Au—TiO₂ coating at a faster rate than what occurs with the pristineuncoated fiber material.

As shown in FIG. 9, the breakdown of methylene blue proceeds much morerapidly for the fiber samples that have been coated with TiO₂, andfurther improvement of the rate of decay is obtained when gold or silvernanoparticles are deposited on the TiO₂-coated fibers. FIG. 9illustrates the integration of the area contained by the peaks in FIG. 8and allows for determination of the rate of stain removal from thetextile materials. The rate of stain removal observed for the Ag/Au—TiO₂coated fiber materials is of the first order, and was observed toproceed more rapidly for the Ag/Au—TiO₂ coated fiber materials than foreither the only TiO₂ coated fiber materials or the untreated fibermaterial, providing direct quantitative verification of the enhancementin photocatalytic activity obtained with this treatment methodology. Theextinction of methylene the adsorbed stain can be seen to follow aroughly first order rate of decay, where the rate of decay can bedetermined by ln([C]/[C]₀)=−kt (illustrated by the plot of FIG. 9).

FIG. 10 illustrates repeated testing cycles of the Ag/Au—TiO₂ coatedfiber materials to illustrate that the photocatalytic activity of theAg/Au—TiO₂ coated fiber materials does not decrease over time. As shown,following three cycles of staining followed by exposure to simulatedsunlight until the stain was virtually eliminated, the Ag/Au—TiO₂ coatedfiber materials displayed remarkable consistency of stain removal overmultiple cycles, with the obtained rate constants of stain removal beingvirtually the same. As further illustrated by FIG. 10, the kinetic ratesof stain degradation do not change over multiple staining cycles for theAg/Au—TiO₂ coated fiber materials, and the photo-catalytic activity ofthe produced Ag/Au—TiO₂ coating is stable even over a significant lengthof time.

FIG. 11 illustrates FTIR spectra of the Ag/Au—TiO₂ coated fibermaterials after repeated exposure to simulated solar light for exposuretimes of (a) no exposure, (b) two hours, (c) four hours, (d) six hours,and (e) ten hours. As shown, the spectra for the Ag/Au—TiO₂ coated fibermaterials remains unchanged over time indicating minimal degradation.Additionally, the surface coating is not being damaged during theprocess of stain removal, and the photocatalytic activity of theAg/Au—TiO₂ coated fiber materials appear to remain roughly unchangedover multiple staining/stain removal events. The concentration of thestain also has no apparent effect on the rate of stain removal, asstaining for the first two cycles was performed using a 0.001% w/vmethylene blue solution, and staining for the third cycle used a 0.1%w/v solution and no difference in extinction rate was observed. Thissuggests that the photocatalytic activity of the Ag/Au—TiO₂ coating doesnot decrease with increased stain saturation, at least at practicallevels of staining.

Staining with Congo red was also performed to evaluate thephotocatalytic performance with a different, less easily broken-downstain. In general, the extinction of Congo red can be seen to proceedmore slowly than methylene blue, with the rate of extinction of Congored stained on pristine fiber material being roughly half that ofmethylene blue stained on pristine fiber material. The improvement inthe rate of stain extinction of the Ag/Au—TiO₂ coated fiber materialsover the pristine fiber material was also less pronounced when Congo redwas tested, with a 1 mM Ag/Au—TiO₂ coated fiber material sampledemonstrating the best performance in this case with a 65% improvementin the rate of stain removal when compared to the pristine fibermaterial. Congo red taking longer to degrade is expected as it has beenfound to take roughly twice as long as methylene blue tophotocatalytically degrade, however the decrease in the photocatalyticeffect of the Ag/Au—TiO₂ coated fiber materials is notable. This effectcan be partially accounted for by the fact that Congo red, while havingits main absorption peak at 496 nm, also has two absorption peaks in theUV region at 236 and 338 nm. Because of this, it is likely that some ofthe incident photocatalytically useful UV and near UV radiation wasabsorbed by the Congo red stain itself rather than interacting with theAg/Au—TiO₂ coating layer, decreasing the apparent efficiency of thecatalytic coating. Compounds such as Congo red which absorb high-energyincident radiation are a good example of why Au/Ag nanoparticle-basedphotosensitizers are important for photocatalytic applications; bydecreasing the bandgap of TiO₂ and increasing the wavelength range inwhich photons can be harnessed for photocatalysis, compounds whichinherently absorb high-energy incident photons can still be degraded.This is likely the reason that the majority of the nanoparticle coatedsamples displayed better performance than the fiber material coated withTiO₂ only when stained with Congo red.

Additionally, the Au—TiO₂ coated fiber materials displayed markedlybetter photocatalytic activity than the Ag—TiO₂ coated fiber materialswhen stained with Congo red (S7), and the reason for this could beexplained by the higher wavelength of the gold nanoparticle peakrelative to the silver peak, and thus the decreased overlap with theCongo red peaks. This strongly suggests that electron transfer is takingplace between the gold nanoparticles and the TiO₂ coating, and that thegold nanoparticles are acting as photosensitizers. A complicating factorin interpreting the kinetic data directly is the non-first order rate ofstain extinction observed for the samples not impregnated withnanoparticles, which was also observed in previous works. Thiscomplicates direct comparison of the kinetic constants with one anotherhowever qualitatively it can still be seen that the rate of stainextinction is improved for the metallic nanoparticle impregnated samples(See FIG. 8).

The fiber materials' stability of photocatalytic activity over time, andconfirmation that the cellulose was not being photocatalyticallydestroyed was provided by FTIR analysis of the Au—TiO₂ coated fibermaterials at regular intervals after UV exposure (See FIG. 11).Degradation of the fiber would be evidenced by changes in the FTIRspectra corresponding to destruction of the cellulosic backbone, howeverno changes in the spectra are observed. Characteristic peaks that can beobserved include a broad O—H stretching band at 3378 cm-1, the C—Hstretching band at 2900 cm-1, and the H—O—H bending band at 1650 cm-1,which is observed to be more intense in the Au—TiO₂ coated fibermaterial than in the pristine fiber material, however this may also bedue to the somewhat hydrophobic nature of the potassium bromide used toprepare the fibers for FTIR analysis. The TiO₂ band is expected toappear at ˜700 cm-1, and indeed the Au-TiO₂ absorption spectra lack the“dip” observed in the spectra of pristine cotton near 700 cm-1, whichsuggests that the TiO₂ while not immediately visible is indeed presentas a relatively broad peak. Reduction of the intensity of C—H stretchingband at 2900 cm-1 was also observed. Overall, the consistency of theFTIR spectra after ten hours of exposure to simulated solar lightsuggests that the Au—TiO₂ coated fibers possesses long-term photostability.

Referring to FIGS. 12 and 13, the antimicrobial properties of theprepared fabric material were examined via the Kirby-Baur disk diffusionmethod using gram negative E. coli. bacteria. The nanoparticle coatedfiber samples are expected to show antimicrobial activity in addition tothe stain cleansing properties. As shown in FIG. 12, a zone of exclusionis clearly visible around the Au—TiO₂ coated fiber material (a) and thesemiconductor and Ag—TiO₂ coated fiber material (b), but not around theTiO₂ coated fiber material alone (c), indicating that the metallicnanoparticles directly grown on the semiconducting surface lend thematerial antimicrobial properties.

Testing of the anti-microbial properties of the Ag/Au—TiO₂ coated fibermaterials demonstrated that the prepared fiber samples were resistant togram negative E. coli microbial contamination as evidenced by the zoneof inhibition that was present around the fibers after inoculation andincubation of the plates (See FIG. 12). It should be noted that thedegree of coli inhibition for the gold and silver nanoparticle coatedsamples was about equivalent. This result was expected given thewidespread study and utilization of silver nanoparticles for theirbactericidal properties, and the recent utilization of goldnanoparticles for the same purpose. The TiO₂ and pristine cotton fibermaterial samples exhibited little to no bacterial inhibition, which isnotable as some limited degree of bactericidal activity would beexpected simply from the reducing/oxidizing potential generated by theTiO₂ layer, and while the oxide alone likely generates someantimicrobial activity, it is apparently much more pronounced with thegold and silver nanoparticle containing samples. It is likely howeverthat bacteria located directly on the illuminated fiber samples coatedwith TiO₂ only would be quickly removed by the oxidizing power of theTiO₂ and the reactive species generated at the surface, as E. coli,Staphylococcus aureus, and Pseudomonas aeruginosa, the bacteriaresponsible for common skin infections/MRSA (methicillin-resistantStaphylococcus aureus) and hospital-acquired antibiotic resistantinfections respectively, have each been experimentally observed to bekilled rapidly on illuminated TiO₂ surfaces.

Furthermore the toxic compounds produced by bacteria can themselves becertainly decomposed by the catalytic action of TiO₂. However, thislocalized effect is insufficient if the fiber is to be deployed asclothing material, as the entirety of the fiber should be kept free frommicrobes, not just the outermost exposed surface, thus the relativelylarge zone of exclusion provided by the incorporation of gold and silvernanoparticles is desirable. One proven mechanism of bactericidal actionfor both gold and silver nanoparticles includes the disruption ofcysteine/disulfide bonds in the proteins on the exterior of bacterialcell walls leading to decreased cell wall integrity, direct inhibitionof ATP production, ribosomal activity, and DNA degradation.

Free radical generation has also been proposed to be an activebactericidal mechanism for silver nanoparticles. The reaction betweensilver nanoparticles and the membrane structures of both gram positiveand gram negative are not fully understood, however the formation of“pits” in the out membranes due to the presence of silver nanoparticles,leading to increased membrane permittivity and ultimately cell deathhave been observed. However there remains a strong argument for the freeradicals generated by silver nanoparticles to be the main causalmechanism behind the antimicrobial effects, as the inclusion of anantioxidant in one study was found to eliminate the anti-microbialaction of silver nanoparticles. Furthermore it has been suggested thatthe evolution of silver ions produced from the silver nanoparticles viatheir oxidation by the holes produced on the TiO₂ layer may be anothermechanism by which the TiO₂/Ag nanoparticle hybrid surface exhibitsantimicrobial activity, as a similar mechanism has been observed withTiO₂/copper hybrid surfaces. Our results suggest that some combinationof the above outlined plays an active role in improving theantimicrobial activity of the nanoparticle coated fiber samples, andfurther elucidation of the mechanism behind the observed antimicrobialproperties could be had testing the nanoparticle coated fibers in thepresence of an antioxidant. The gold and silver nanoparticle coatedfiber materials showed similar antibacterial activity. FIG. 13demonstrates the mechanism behind the most active bactericidal pathwayin this photocatalytically active material, namely, the generation ofelectrons and holes that react through the mechanisms outlined above todestroy bacteria in proximity to the photocatalytically activenanostructured surface.

In some embodiments, the method provides for treating a textile fibermaterial with a sol-gel based method, as outlined above, so as tofacilitate the deposit of a semiconducting thin film (TiO₂) on at leastone surface of the textile material. In this manner, metallic (Ag/Au)nanoparticles, for example silver, gold or both silver and gold,metallic nanoparticles are grown directly on the oxide surface via thephotocatalytic reduction method outlined above. This treatment methodprovides for the creation of a photocatalytically active fiber material,that is scalable using techniques carried out at normal atmosphericpressure (about 1 atmospheric pressure), and require only that thematerial be capable of withstanding 95° C. temperatures for a shortperiod of time. Another important feature of the method 100 is the useof the nanoparticles to allow the absorption and photocatalyticutilization of near-UV and visible incident photons which improvesphotocatalytic activity by allowing for the useful harnessing of moreincident light. The metallic nanoparticles impart an antimicrobialfeature to the surface of a material, for example the surface of a fibermaterial, another unique feature imparted to the surfaces and fibermaterials provided as part of the invention.

The present invention allows for the treatment of fibrous andnon-fibrous textile materials and the production of a hybridsemiconductor/metallic nanoparticle based photocatalytic(self-cleaning), antimicrobial, and UV radiation protective system onthe textile surface. The treatment technique allows the textile materialto be treated without the use of either vacuum or pressurizedconditions, and the textile material is required only to withstand dryannealing at 95° C. and hydrothermal treatment in boiling water, bothmild conditions compared to more exotic treatment methodologies.

While the present invention has been described in terms of particularembodiments and applications, in both summarized and detailed forms, itis not intended that these descriptions in any way limit its scope toany such embodiments and applications, and it will be understood thatmany substitutions, changes and variations in the described embodiments,applications, and details of the method and system illustrated hereinand of their operation can be made by those skilled in the art withoutdeparting from the spirit of this invention.

From the foregoing, it will be seen that this invention is one welladapted to attain all the ends and objects hereinabove set forthtogether with other advantages which are obvious and which are inherentto the structure. It will be understood that certain features and subcombinations are of utility and may be employed without reference toother features and sub combinations. This is contemplated by and iswithin the scope of the claims. Since many possible embodiments of theinvention may be made without departing from the scope thereof, it isalso to be understood that all matters herein set forth or shown in theaccompanying drawings are to be interpreted as illustrative and notlimiting.

The constructions described above and illustrated in the drawings arepresented by way of example only and are not intended to limit theconcepts and principles of the present invention. Thus, there has beenshown and described several embodiments of a novel invention. As isevident from the foregoing description, certain aspects of the presentinvention are not limited by the particular details of the examplesillustrated herein, and it is therefore contemplated that othermodifications and applications, or equivalents thereof, will occur tothose skilled in the art. The terms “having” and “including” and similarterms as used in the foregoing specification are used in the sense of“optional” or “may include” and not as “required”. Many changes,modifications, variations and other uses and applications of the presentconstruction will, however, become apparent to those skilled in the artafter considering the specification and the accompanying drawings. Allsuch changes, modifications, variations and other uses and applicationswhich do not depart from the spirit and scope of the invention aredeemed to be covered by the invention which is limited only by theclaims which follow.

What is claimed is:
 1. A method for providing a metallic nanoparticle,semiconductor-coated surface on a material comprising: providing asemiconducting layer on at least one surface of a material to provide atleast one treated surface on a semi-conductor-coated textile material;depositing metallic nanoparticles onto said treated surface; and forminga metallic nanoparticle, semiconductor-coated surface on the material.2. The method of claim 1, wherein providing a semiconducting layer tothe surface comprises coating the surface with a TiO₂ film.
 3. Themethod of claim 2, wherein coating the surface with the TiO₂ filmcomprises a sol-gel procedure.
 4. The method of claim 1, wherein themetallic nanoparticles comprise gold nanoparticles.
 5. The method ofclaim 1, wherein the metallic nanoparticles comprise silvernanoparticles.
 6. The method of claim 1, wherein depositing metallicnanoparticles onto the surface further comprises: preparing a solutionof metallic nanoparticle precursor solution; immersing saidsemiconductor-coated textile material in said precursor solution toprovide a precursor solution treated material; drying said precursorsolution treated material; and exposing said dried precursor solutiontreated material to ultraviolet radiation for a selected time durationso as to provide deposition of metallic nanoparticles on at least onesurface of the material.
 7. The method of claim 6, wherein saidprecursor solution comprises gold chloride (AuCl₃) and ultrapure water.8. The method of claim 6, wherein said precursor solution comprisessilver nitrate (AgNO₃) and ultrapure water.
 9. The method of claim 6,wherein said semiconductor-coated textile material is immersed in saidprecursor solution for approximately 30 seconds.
 10. The method of claim6, wherein said precursor solution treated material comprises aprecursor solution treated semiconductor coated fiber material.
 11. Themethod of claim 10 wherein the precursor solution treated semiconductorcoated fiber material is dried at room temperature under normalatmospheric conditions for approximately 24 hours, to provide apretreated dried semiconductor coated fiber material.
 12. The method ofclaim 11, wherein said pretreated dried semiconductor coated fibermaterial is exposed to about 254 nm UV radiation for approximately 30minutes.
 13. The method of claim 11, wherein said pretreated driedsemiconductor coated fiber material is exposed to about 254 nm UVradiation for approximately 15 minutes.
 14. A material comprising atleast one surface comprising a metallic nanoparticle,semiconductor-coated surface, wherein said surface is anti-microbial andself-cleaning.
 15. The material of claim 14 wherein the metallicnanoparticles comprise gold nanoparticles, silver nanoparticles, or acombination thereof.
 16. The material of claim 14 wherein the surface isa textile surface.
 17. A metallic nanoparticle and semi-conductor fibermaterial comprising: a textile material having at least one surfacecomprising a nanostructured titanium dioxide film, wherein saidnanostructured titanium dioxide film comprises a metallic nanoparticle.18. The metallic nanoparticle and semi-conductor coated film material ofclaim 17 wherein the metallic nanoparticle comprises a gold, silver orcombination of gold and silver nano-particles.
 19. The metallicnanoparticle and semi-conductor coated film material of claim 17 whereinsaid material is resistant to E. coli microbial contamination.